1. Field of the Invention
The present invention relates to dye precursors as novel compounds which act effectively.
Further, the present invention relates to a monocolor or multicolor image forming material which is used for various light sources emitting light having wavelengths from UV to near-infrared rays, and an image forming method using the same, and more particularly to an image forming material which is excellent in sensitivity, light-fastness of image, hues in image areas, and whiteness at non-image areas, and an image forming method using the same.
2. Description of the Related Art
Heretobefore, various types of dry type image forming methods which do not use liquid type developers and the like, and which do not produce waste materials have been researched. Among these, methods in which a composition to be hardened with light are used as components in an image forming layer of a recording material (image forming material) are attracting notice.
This method is characterized in that the composition to be hardened with light contained in the image forming layer are hardened through an exposure process so that a latent image is formed, while components, which are contained in unexposed portions of the image forming layer and which contribute to a color-forming reaction, are heated and/or pressurized so as to move inside the image forming layer so that an image produced through color formation is formed. In a case of using a recording material in such a method as described above, first of all, light is transmitted, through an image original, to expose a recording material, and then the exposed portion is hardened so that a latent image is formed. Thereafter, this recording material is heated or pressurized so as to move the components which are contained in unhardened portions (unexposed portions) of the layer and which participate in a color-forming reaction, thus forming a visible image.
As an example of such a recording material as described above, a recording material disclosed in Japanese Patent Application Laid-Open (JP-A) No. 61-123838 is known. Namely, the recording material is formed by laminating a layer which contains therein photopolymerization components formed of a vinyl monomer having acidic groups and photopolymerization initiators; an isolation layer; and a layer which is formed by electron donative colorless dyes. In a case of this recording material, the acidic groups do not diffuse under heat at non-image areas, namely, in portions which are hardened through a photopolymerization reaction, and thus problems in which non-image areas become colored do not occur. However, problems have arisen in that image density is low and light-fastness is low.
Examples of recording materials in which image density is improved are disclosed in JP-A Nos. 3-87827 and 4-211252. The former is a recording material which has an image forming layer in which one of two components of a two-component type photosensitive and heat-sensitive color-forming recording material is contained in microcapsules, and the other is contained in portions outside the microcapsules of the image forming layer (1) as hardening compounds of photo-curing type composition, or (2) together with the photo-curing type composition. The latter is a photosensitive and heat-sensitive recording material which comprises a support, and a layer applied on the support, the layer including: microcapsules which contain electron donative colorless dyes; and outside of the microcapsules, a photo-curing type composition which contains electron acceptive compounds, polymerizable vinyl monomers, and photopolymerization initiators. However, since both of the examples use electron donative colorless dyes which are so-called phthalide compounds, as dye precursors, a satisfactory level of light-fastness is not attained in the images.
In a similar manner to the above description, as an example of a photosensitive and pressure-sensitive paper, recording materials disclosed in Japanese Patent Publication (JP-B) Nos. 64-7378, 64-7377, and 64-7376 are known. However, since dye precursors used in these recording materials are also phthalide compounds, a sufficient level of light-fastness is not attained in the images of recording materials of these examples.
A heat-type image forming method is disclosed in JP-B No. 5-42359. The heat-type image forming method is such that a recording material, which has an image forming layer containing compounds which have carbamate portions that are instable under heat and which cause irreversible monomolecular division, is heated imagewisely, and the compounds decompose with heating so as to form a visible image. In this method, dye precursors other than phthalide compounds can be used. However, since the dye precursors form color by heating alone, a large amount of heat must be used when images are written, thus causing problems such as requiring a large-size image forming apparatus and delaying a processing rate. Further, there has been a problem in that non-image areas become fogged by remaining or accumulated heat during image writing. Since color-formation is controlled by heating alone, even in terms of storage stability over time, there has been a problem in that the non-image areas tend to become fogged.
Japanese Patent No. 2744101 discloses a heat-sensitive element. In the heat-sensitive element, dye precursors which are substituted by protective groups which are thermally eliminable when heated and by elimination groups which are eliminated irreversibly when heated are heated imagewisely so that images are formed. Also in this case, since color formation is controlled by heating alone, there has been almost the same problem as in the heat-type image forming method which is disclosed in the aforementioned JP-B No. 5-42359. Further, because images produced through color formation are not fixed in the image forming layer, there have been problems with storage stability over time. For example, when heat is applied to the heat-sensitive element having an image thereon, there has been a problem in that dye precursors in non-image areas of the image forming layer decompose gradually, which leads to fogging.
Namely, it is desired to provide dye precursors which form color due to elements other than heating, or through action of another element in combination with heating.
Various types of photosensitive and heat-sensitive photographic materials using dye precursors are disclosed in JP-A No. 5-204087, and in Japanese Patent Application National Publication (Laid-Open) Nos. 8-507885 and 10-502460. However, since silver halides are used as photosensitive materials, from the viewpoint of storage stability and handling, they are not suitable. Therefore, it has been desired to obtain an image forming material capable of forming an image through a completely dry processing system in which silver halides are not used (which will be referred to as xe2x80x98non-silver saltxe2x80x99, hereinafter).
It is an object of the present invention to provide dye precursors which are novel compounds having the characteristic of forming color due to elements other than heating, or through action of another element in combination with heating.
Further, it is another object of the present invention to provide a monocolor or a multicolor non-silver salt type image forming material and an image forming method using the same, wherein various light sources emitting light of wavelengths of each range from UV to near-infrared rays can be used in a full-dry processing system in which use of developing solutions is not needed, and which does not produce waste materials, and wherein images which are excellent in sensitivity, image quality, and light-fastness can be formed.
Further, the above-described objectives can be accomplished by the present invention which will be described hereinafter. Namely, a first aspect of the present invention is to provide dye precursors as novel compounds. Specific examples of these dye precursors include two types of dye precursors as follows.
(Dye Precursor A)
A dye precursor for forming color through contact with base, and which is represented by the following formula (1): Formula (1): 
wherein Ar represents an aromatic ring or a heterocyclic ring, each of which may have a substituent; Cp represents a coupler residue; and L represents a protective group which can be eliminated by a base.
(Dye Precursor B)
A dye precursor for forming color through contact with a base, and which is represented by the following formula (2): Formula (2): 
wherein Ar represents an aromatic ring or a heterocyclic ring, each of which may have a substituent; Cp represents a coupler residue; L1 represents a protective group which can be eliminated by a base; and L2 represents an elimination group or a protective group which is eliminated after L1 is eliminated.
Each of these dye precursors can form color by having a base act upon the dye precursor at room temperature or within a range of temperature at which it is impossible for the dye precursor to form color without a base even if the dye precursor is heated. By using these dye precursors in an image forming layer of an image forming material, an image forming material which can exhibit excellent color formation with a small amount of energy and images with extremely excellent storage stability can be obtained.
A second aspect of the present invention relates to an image forming material and an image forming method using the same, and more particularly to an image forming material comprising an image forming layer and a support, the image forming layer being disposed on the support and containing at least one type of each of a photopolymerization initiator, a dye precursor which can form color through contact with a base, a base or a base precursor, and a polymerizable compound.
According to the second aspect of the present invention, the image forming material has high photo-sensitivity although it is a non-silver salt image forming material, and can provide an image which is excellent in hues and light-fastness. Further, the obtained image can be fixed as an image with excellent light-fastness by polymerizing both image portions and background portions (non-image areas). The image forming material is irradiated with light imagewisely, the polymerizable compound is polymerized by radicals which generate at light-irradiated portions from a radical generating agent. Accordingly, the light-irradiated portions are hardened, and the base or base precursors in vicinities of the light-irradiated portions are fixed in their respective positions so that a latent image is formed (latent image forming process). Thereafter, the entire surface of the image forming layer is heated and/or pressurized so that a color-formed image is formed in accordance with the latent image (developing process). As a result, an image forming method which is excellent in terms of sensitivity and high processing speed, which does not use developing solutions and which does not produce waste material, can be provided. The entire surface of the image forming layer is irradiated with light as needed and images are fixed on the layer (fixation process) so that images with superior light-fastness can be formed.
In the second aspect of the present invention, since the dye precursor which can form color through contact with a base is used, in contrast to an image forming material which uses dye precursors which form color by heating alone, the image forming material of the present invention is characterized in that non-image areas are not likely to be fogged. By setting the temperature at which the entire surface of the image forming layer is heated to a temperature at which it is impossible for the dye precursor to form color without a base even if the dye precursor is heated, a non-image area does not become fogged even when the entire surface of the image forming layer is heated.